Cinétique d’infestation par Haemonchus contortus et réponse d’ovins de races résistante (Martinik Black Belly) et sensible (Lacaune)

The extension of resistance of gastrointestinal nematodes to anthelmintics, recently observed in Haemonchus contortus, represents a real problem and makes it urgent to find alternative solutions such as the selection of helminth-resistant animals. All cases of experimental infestations show significant individualvariability in egg excretion, allowing good discrimination between resistant and susceptible individuals, which enables selecting resistant individuals in the studied breeds. However, the lack of knowledge on immune response mechanisms in sheep worms is an obstacle to the development of this selection. It is known that the excretion level of parasite eggs in feces is a relevant indicator for assessing the resistance of an animal to worms. This criterion was examined in the present study carried out with two French sheep breeds, the Martinik Black Belly (resistant) and the Lacaune (sensitive). The sheep were infested orally with a single dose of 10,000 L3 larvae of H. contortus. The sheep response was monitored during antemortem and postmortem examinations. The results clearly showed that during a first H. contortus infestation there was a significant difference between the parasite populations (parasite intensity and egg production) and between certain pathophysiological parameters (blood and tissue eosinophilia) observed in the two sheep breeds.